In order to cope with various forums and new technologies related to the 4th generation mobile communications, the 3rd Generation Partnership Project (3GPP) who enacts the technical standards of 3G mobile communication systems has proceeded with studies on the Long Term Evolution/System Architecture Evolution (LTE/SAE) technologies since the end of 2004 as a part of the effort to optimize and enhance the performance of 3GPP technologies.
The SAE led by 3GPP SA WG2 is a study on network technologies for the purpose of determining a network structure together with the LTE work of 3GPP TSG RAN and supporting mobility between heterogeneous networks. In recent years, the SAE has been considered one of the latest important standard issues in 3GPP. It is a work to develop a system supporting various radio access technologies on the basis of 3GPP IP systems, and has been progressed to aim at an optimized packet based system that minimizes a transmission delay with enhanced transmission capability.
A high-level reference model defined by 3GPP SA WG2 includes a non-roaming case and roaming cases having various scenarios, and the detailed description thereof is given in 3GPP standard documents TS 23.401 and TS 23.402. In FIG. 1, there is illustrated a structural diagram of a network in which the model is schematically reconfigured.
FIG. 1 is a structural diagram illustrating an evolved mobile communication network.
One of the distinctive characteristics of the network structure of FIG. 1 is that it is based on a 2-tier model having an eNode B of the Evolved UTRAN and a gateway of the core network. The eNode B has a similar function, although not exactly the same, to the eNode B and RNC of the existing UMTS system, and the gateway has a function similar to the SGSN/GGSN of the existing system.
Another distinctive characteristic is that the control plane and the user plane between the access system and the core network are exchanged with different interfaces. While one lu interface exists between the RNC and the SGSN in the existing UMTS system, two separate interlaces, i.e., S1-MME and S1-U, are used in the Evolved Packet Core (SAE) system since the Mobility Management Entity (MME) 51 taking charge of the processing of a control signal is structured to be separated from the gateway (GW). For the GW, there are two types of gateways, a serving gateway (hereinafter, ‘S-GW’) 52 and a packet data network gateway (hereinafter, ‘PDN-GW’ or ‘P-GW’) 53.
FIG. 2 is a view illustrating a relation between (e)NodeB and Home (e)NodeB.
In the 3rd or 4th generation mobile communication systems, attempts continue to increase their cell capacity in order to support high-capacity and bi-directional services such as multimedia contents, streaming, and the like.
In other words, with the development of communication and widespread multimedia technologies, various high-capacity transmission technologies are required, and accordingly, a method of allocating more frequency resources is used to increase radio capacity, but there is a limit to allocate more frequency resources to a plurality of users with restricted frequency resources.
In order to increase cell capacity, there has been an approach in which high frequency bandwidth is used and the cell diameter is reduced. If a cell having a small cell radius such as a pico cell is applied, it is possible to use a higher bandwidth than the frequency that has been used in the existing cellular system, thereby providing an advantage capable of transmitting more information. However, more base stations should be installed in the same area, thereby having a disadvantage of high investment cost.
In recent years, a femto base station such as Home (e)NodeB 30 has been proposed among the approaches for increasing cell capacity using such a small cell.
Studies on the Home (e)NodeB 30 have been started by 3GPP Home (e)NodeB WG3, and also in recent years, actively proceeded by SA WG.
The (e)NodeB 20 illustrated in FIG. 2 corresponds to a macro base station, and the Home (e)NodeB 30 illustrated FIG. 2 may be a femto base station. This specification will be described based on the terms of 3GPP, and the term (e)NodeB is used when referring to both NodeB and eNodeB. Also, the term Home (e)NodeB is used when referring to both Home NodeB and Home eNodeB.
The interface illustrated in a dotted line denotes the transmission of control signals between the (e)NodeB 20 or Home (e)NodeB 30 and the MME 51. Also, the interface illustrated in a solid line denotes the transmission of data of the user plane.